In a UMTS (Universal Mobile Telecommunications System) network, for the purposes of improving spectral efficiency and improving the data rates, system features based on W-CDMA (Wideband Code Division Multiple Access) are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). For this UMTS network, for the purposes of further increasing high-speed data rates, providing low delay and so on, long term evolution (LTE) has been under study (see, for example, Non Patent Literature 1). In LTE, as multiplexing schemes, OFDMA (Orthogonal Frequency Division Multiple Access), which is different from W-CDMA, is used on the downlink, and SC-FDMA (Single Carrier Frequency Division Multiple Access) is used on the uplink.
In a third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in the LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. Furthermore, in the UMTS network, for the purpose of achieving further broadbandization and higher speed, successor systems to LTE have been under study (for example, LTE Advanced (LTE-A)). Accordingly, in the future, it is expected that these multiple mobile communication systems will coexist, and configurations (radio base station apparatus, mobile terminal apparatus, etc.) that are capable of supporting these multiple systems will become necessary.
Also, in LTE-A, uplink single-user MIMO (Multiple Input Multiple Output) transmission is introduced to make possible improved uplink spectral efficiency. Consequently, in relationship to this introduction of uplink SU-MIMO, a resource allocation method for a response signal for retransmission of a signal in which a plurality of layers are space-multiplexed on the uplink, is under study.